In electrochemical cells many of the compounds useful as the cathode active materials, are nonconducting. For improved discharge characteristics the nonconductive active materials are generally admixed with electrochemically inert conductive materials, and/or pressed onto an inert conductive grid, or a conductive metal layer is formed on the surface of the cathode. The added conductive material, grid or layer is unreactive with the active cathode material in order to prevent the self-discharge of the cathode. The increase in conductivity is, however, weighed against the decrease in energy density brought about by the addition of the inert materials to the cathode.
In many electrochemical cells the added conductive material, in addition to increasing electrode conductivity, performs other functions. For example, in cells containing a nonconductive mercury compound as one of the components of the cathode, silver (electrochemically inert to mercury compounds) has been added to both improved cathode conductivity and also to immobilize the free elemental mercury formed within the cell during cell discharge. The elemental mercury is a mobile conductive liquid in the cathode and can migrate from the cathode into other parts of the cell thereby possibly short circuiting the cell. The silver within the cathode however immobilizes the liquid mercury by amalgamating with it.
In many mercury cells the added material has not, however, been completely successful in immobilizing all of the mobile mercury produced. Simply adding more amalgamating materials is undesirable, since such added materials reduce cell capacity. In addition, silver, the most commonly used material has become more costly with increased amounts of added silver thereby prohibitively increasing the cost of finished cells.